The present invention relates to a field-effect semiconductor device which has a novel construction and which is based upon a novel operating principle.
In recent years, compound semiconductors made of elements from Groups III and V have been used in attempts to realize a monolithic integrated circuit (IC) with a higher operating speed than a silicon IC because these compounds have a high electron mobility. At present, a typical IC using these semiconductor compounds is composed of N-channel field-effect transistors (FET).
For reducing power consumption, however, it is advantageous to fabricate an IC with complementary transistors. Nevertheless, even if they can be used, complementary transistors cannot be expected to operate at high speed because their hole mobility is low.
If a semiconductor other than the Group III-V compound semiconductor is used as a high hole mobility material, P-channel and N-channel field-effect transistors operating at high speed cannot be combined into a monolithic IC. There, it is advantageous to devise a field-effect transistor which acts as both an N-channel element and a P-channel element. Such a field-effect transistor permits the easy formation of complementary transistors in a monolithic IC.
A typical field-effect transitor acting as both an N- and P-channel element in the prior art is disclosed in U.S. Pat. No. 3,283,221 granted to Frederic P. Heiman. In this patent, the channel portion of a field-effect transistor having an MOS (Metal-Oxide-Semiconductor) structure is formed by diffusion or vapor growth of superimposed P- and N-type silicon layers. This structure uses silicon which has a low electron mobility, so that the N-channel transistors cannot be expected to operate at high speed. In the specification of the patent, it is also disclosed that the channel portion may be made of a semiconductor other than silicon, and may have its P- and N-type layers made of different substances. However, at best that disclosure only hints at the possibility, but fails to provide any specific details.